Method for cleaning jet and gas turbine engines



L. J. FULLER Aug. 9, 1960 METHOD FOR CLEANING JET AN GAS TURBINE ENGINES 2 Sheets-Sheet 1 Original Filed March 4, 1955 Nm Nm. ww

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NNNNN Aug. 9, 1960 L. J. FULLER 2,948,092

METHOD FOR CLEANING JET ANU GAS TURBINE ENGINES original Filed March 4, 1955 f 2 sheets-snee: 2

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ATTORNEYS` itUnited States Patent METHOD FOR CLEANING JET AND GAS TURBINE ENGINES Lawrence J. Fuller, Box 124, R.D. 1, Norristown, Pa.

Original application Mar. 4, 1955, Ser. No. 492,280. Di-

vided and this application Apr. 26, 1956, Ser. No. 580,943

12 Claims. (Cl. 51-282) The present invention relates to methods for cleaning jet, turbo jet, turbo prop, gas turbine and other engines which have air compressors and utilize large quantities of air.

The present application is a division of my copending application, Serial No. 492,280, tiled March 4, 1955, now abandoned, for Method and Apparatus for Cleaning let and Gas' Turbine Engines.

A purpose of the invention is to clean an engine of the character referred to without disassembly and without interruption in service.

A further purpose is to restore to a turbo jet engine or similar engine substantially` all of the eiciency lost through build up on its operating surfaces.

A further purpose is to clean a turbo jet or similar engine by a method which will not harm the critical surfaces, and which can be used repeatedly as part of the ordinary maintenance of the engine.

A further purpose is to remove products of corrosion from operating surfaces of a turbo jet or similar engine.

lFurther purposes appear in the specification and in the claims.

In the drawings I have chosen to illustrate only a few of the numerous embodiments in which my invention may appear, selecting the forms shown from the standpoints of convenience in illustration, satisfactory operation and clear demonstration of the principles involved.

Figure 1 is a diagrammatic central longitudinal halfsection illustrating a gas turbine to which the method of the invention has been applied. p

Figure 2 is a view similar to Figure l illustrating a modification.

lFigure 3 is a front elevation partly in axial section showing a feeding mechanism for the cleaning material which may be conveniently used in the present invention; l

Figure 4 is a side elevation illustrating the mechanism of Figure 3.

Describing in illustration but not in limitation and referring to the drawings:

J et, turbo jet, turbo prop, gas turbine and other similar engines using large quantities of air are subject to relatively rapid loss in power due to build up on compressor blades, deposits in the combustion chamber and fouling of the turbine blades.

The build up on compressor blades appears to be due to accumulation of line airborne solids such as dust, insects, salt deposits and film-forming vapors, such as oil vapors, which act as a binder.

Also, compressor blades commonly made from straight chrome stainless steel are subject to certain surface corrosion attack under particular conditions which lowers the operating etiiciency of the Vcompressor and' is believed, at least by some authorities, to lead to intergranular corrosion and subsequent failure of thecompressor blades.

The eiciency of the turbine is alsoV impaired because the blades becomeffouled by the lburninglof fuel which ice contains corrosive and deposit-forming materials, such as compounds of sodium or of vanadium. The turbine blades also are affected by hot gases which pass through the turbine, their temperature sometimes rising above recommended operating temperatures.

In the past the procedure usually followed to remove deposits and products of corrosion has involved a general overhaul of the engine with accompanying disassembly of the engine.

Attempts have been made to clean engines by introducing organic liquid solvents in the air intake stream of the air compressor, but these methods have not been eiiective for removing most types of build Iup and did not remove corrosion products. This procedure is also subject to the difiiculty that most of the cleaning is concentrated on the outer ends of the blades due to the centrifugal effect of the compressor turbine rotors on the liquid.

Efforts have also been made to use ground walnut shells as a cleaning material introduced into the air intake, but this procedure has not produced satisfactory results for cleaning most types of build up. The cleaning accomplished by ground walnut shells is limited to the first few stages of the air compressor. The stages further back in the compressor have a build up which becomes baked into a hard varnish due to elevated temperatures encountered in these stages and this deposit cannot be removed by the action of ground walnut shells or ground peach pits or other organic cleaning material.

A further serious disadvantage of organic materials is that the organic materials burn while passing through the combustion chamber and therefore they are not effective in removing deposit from turbine blades.

I have discovered that engines such as jet, turbo jet, gas turbine, turbo prop and other similar engines can be cleaned effectively and restored in engine efliciency by introducing a suitable finely-divided inorganic cleaning material into the intake air stream of the engine compressor while the engine is in operation.

A wide variety of suitable cleaning materials may be selected, providing proper attention is paid to the required characteristics as set forth herein.

The inorganic cleaning material used must be substantially free from materials which would normally be considered abrasives to metals. By contrast it should be of a low hardness number and low abrasiveness and should be free from impurities that are abrasive. An indication of what is intended by this requirement will be evident from the characteristics of the specific materials set forth below.

It is also important that the inorganic cleaning material should not soften, fuse or burn, that is, undergo combustion at temperatures up to l600 F. and preferably should not soften, fuse or burn at temperatures up to 1800 F.

It is also desirable that the cleaning material have a crystal formation which provides sharp or rough crystal contours, the projections of the crystals contributing to the effectiveness of the cleaning action 'of the material being relied upon for the cleaning action. By the same token the material should readily undergo fracture and the fractured crystals should likewise not be rounded but should have a sharp, jagged rough surface.

The particle size of the inorganic cleaning material should be small enough so as not to interfere with passage of stator and rotor blades, and good practice indicates that the particle size should be below 30 mesh and preferably in most engines below 6() mesh. However, granules of the material c-an vary depending on engine design and fragility of cleaning material. The mesh referred to herein are Tyler standard mesh per linear inch.

additional helpful characteristic that is desirable in cleaning materials is a microcrystalline structure Whose crystals have sharp surfaces such as needle shaped microcrystalline-material. v

In some cleaning material it is desirable to have a certain amount of free or combined water of crystallization to absorb heat while passing through the combustion chamber and prevent softening or fusing. The water of crystallization may be crystallization, water of chemical comcombination or adsorbed water.

It is also very desirable to use a cleaning material which has the property of absorbing liquids such as tars, petroleum oils and the like which often will form parts of gummy deposits when an oil leak develops in engine operation.

A preferred cleaning material will be hydrous aluminasilica or aluminous minerals, satisfactory cleaning materials being fullers earth, bentonite, bauxite or mixtures thereof.

Engine design varies and materials used in air compressor and turbine blades also vary widely. To suit these conditions cleaning materials can be varied even to the addition of organic material along with the inorganic materials. v

When I make reference herein to the feeding of my inorganic cleaning materials, I do not necessarily intend to exclude the presence of an accompanying organic cleaning material. In most of todays engines it will not contribute to the cleaning operation and may, in most instances, slow up the action of the cleaning material.

Cleaning materials must be carefully prepared by grading, grinding, screening and sometimes calcining. Also precaution must be exercised to prevent contamination and inclusion of oversize hard objects. Roasting or calcining should be regulated to permit the proper amount of free and combined water to remain in the material to give it the properties necessary for a successful cleaning operation.

In some cases however when engines are equipped with intercoolers between air compressors moist conditions are encountered which require cleaning materials that do not cake when becoming wet, and in such cases calcining is desirable.

As already explained, it will be evident that the cleaning material of the invention does not tend to form smooth or rounded particles even after it has been impinged against the blades of the engine.

A further advantageous characteristic of the cleaning material is its low specific gravity so that it can readily be airborne even in comparatively large particle sizes. This feature is true of fullers earth, bauxite and bentonite.

The cleaning material is fed into the intake of the air compressor (airborne air stream) at a controlled rate while the engine is in operation. In order to clean the blades in all stages of the air compression it is best to v-ary the engine speed during cleaning operation. The speed should range from low to high.

I illustrate in Figures 3 and 4 a suitable feeding mechanism in accordance with the invention. A hopper 20 containing the cleaning material has vat the bottom a discharge opening 21 which connects to the side of a feed chamber 22 in which a screw conveyor 23 operates. The screw conveyor is driven by hollow shaft 24 which is operatively connected to speed reducer 25 driven by a belt and pulley combination 26 from a variable speed drive unit 27. The extension of hollow shaft 24 also carries a pulley 28 which drives belt 30 driving pulley 31 on shaft 32. The shaft 32 is mounted in bearings 33 and has a crank 34 which is connected by a pin to a transversely slotted agitating plunger 35 passing through a screen 35'. The movement of the plunger avoids bridging of the cleaning material at the discharge 'opening 21.

An air transporting cavity runs the entire length of screw 23 and its driving shaft 24 which is connected by a rotary coupling 36 to an air hose 37 supplying compressed air from an outside source. Air discharges from the discharge end of worm 23 at a high velocity and forms a venturi at 38 which entr-ains the cleaning material in the air entering transporting 'pipe 40. The pipe 30 is located directly opposite the air discharge opening at the end of the worm. Pipe 40 kcarries the air-borne cleaning material to an advantageous location for discharging the cleaning `material so that it is evenly distributed over the air compressor intake.

In order to obtain uniformly satisfactory results, the operator should have control of the rate of feed by varying the variable speed drive-27 and controlling the amount of compressed air introduced bythe pipe 3f7. As good practice dictates the rateof feed of the cleaning material is regulated to suit `the type and sizeof the engine, the kind of buildup, the time which has elapsed since last cleaning the engine, and other conditions.

As an example `merely of practice successfully used, a gas turbine delivering approximately 5000 H.P. will require from 60 to 160V pounds of cleaning material for a normal cleaning job. The cleaning material should preferably be fed at such a rate that the cleaning job is completed within 20 to 30 minutes, athough longer or shorter cleaning cycles can be used. The above example indicates a rate of feed of approximately one to eight pounds per minute.

A substantial recovery in engine efficiency is possible in accord-ance with the invention if the eciency loss is due to build up on compressor and turbine blades. It has not been uncommon in practice to obtain a horsepower recovery of the order of 20% when a previous drop ofv eiciency of this amount had occurred due to build up.

It is important in accordance with the invention to protect vulnerable parts of the engine against contamination with the cleaning material. These vulnerable parts include particularly main beairngs and the lubrication system.

For best protection a suitable gas, preferably clean air, is brought from any desired source into theengine inner casing at points adjacent the insides of the labyrinth seals between stationary and moving engine parts. The air is introduced in sufficient quantity and -at a sufficient pressure to assure a ow of -air through the seals into the operating gas stream of the engine.

It will'be evident that the spaces surrounding the rotating members and the internal sections of the rotating ele.-

ments are in direct communication with the internal sections of the engine housing where ythe main bearings are located. The labyrinth seals are not adequate to prevent infiltration of cleaning material which would seriously damage the bearings and the lubrication system.

It will further be evident that in some engines additional protection due to the outward flow of air through the labyrinth seals is desirable -at ally times.

The suitable gas to provide the outward flow through the labyrinth seals may be bled from the air compressor and then passed through la iilteror separator to remove the cleaning material before it is introduced into the interior of the engine. As an alternative an outside source of clean air or other gas may be used.

Considering the illustration of Figure 1, an air compressor 41 and a turbine 42 are illustrated consisting of rotating parts of a gas turbine engine. Air enters the air compressor 41 at `43 and passes through the axial flow air compressor section 44 and through the combustion chamber 45. Products of combustion and excess air enter the gas turbine -46 and then escape via the exhaust 47. strated at 48, 50, 51 land 52, as well known, there are labyrinth seals which underv normal conditions prevent excessive quantities of operating gas in the passages of the compressor and the turbine from entering the inner casing'o'f theengine where' main bearings are located at .53, s4, ssandss. The seals, though sufcientfor Operat- At a number of points in theengine suitably illuy ing purposes, are not 100 percent effective in excluding operating gas from entering the inner casing.

To insure positive exclusion of cleaning material, l provide a source of clean gas preferably clean air at 57 which connects by branch pipes 58, 60, 61 and 62 at positions inside of the labyrinth seals and introduces sufficient volume and pressure of air to cause positive outward air ow through the labyrinth seals.

In some cases, as illustrated in Figure 2, it is preferred to introduce the air inside shields 63, 64, 65 and 66 which assure that the air is carried to the vicinity of the bearings before it can ow out through the labyrinth seals.

In order to accomplish a satisfactory cleaning job on the engine, three factors should be kept in mind:

(l1) A satisfactory material should be used as previously set forth.

(2) The material should be properly fed at a controlled rate. Grossly excessive feeding may damage the engine and under-feeding will seriously delay and prolong the operation.

(3) lCritical parts of the engine such as the lubrication system and the bearings must be protected from the cleaning material during the cleaning period. If proper precautions to protect these critical parts of the engine Iare not taken, the effect may be disastrous as cleaning material will get into the bearings and the lubrication system resulting in bearing failure Within a relatively short time.

It will be evident that additional precautions should be taken where the engine design utilizes air from the compressor for atomizing fuel or for other purposes. In this case, the air line for the fuel jets 67 must be connected to an independent source of compressed air, or, if preferred, an air lter or air separator may be used to remove the cleaning material before air passes to the jet.

It will be evident that the cleaning material may if desired be introduced in the engine combustion gases downstream from the compressor.

In view of my invention and disclosure variations and modifications to meet individual whim or particular need will doubtless become evident to others skilled in the art, to obtain all or part of the benefits of my invention without copying lthe method shown, and I, therefore, claim all such insofar as they fall within the reasonable spirit land scope of my claims.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

1. The method of cleaning the internal operative surfaces of turbo jet, turbo prop, gas turbine and similar engines having rotating blades comprising operating the engine, introducing into the intake of the engine an oxidizing gas having generally uniformly suspended finely divided inorganic cleaning material of particles of a size below 30 Tyler standard mesh per linear inch, and having sharp crystalline edges which fracture into sharp crystalline particles to maintain the abrasive characteristics of the particles =and being free from fusing, softening and burning at temperatures as high as 1600 F., moving said oxidizing gas with the suspension of finely divided particles through the turbine under the pressure of the compressor to form a moving atmosphere of suspended particles, rotating the blades of the engine over a range of speeds from high to low speed to move the blades through the particle laden gas to abrade the particles against the blade to remove deposits therefrom and force the particle laden gas through the passages of the engine to remove deposits therein.

2. The method of claim .l which comprises introducing gas into the engine vat points on the inside of the walls and thereby building up a pressure sufficient to cause gas ow through the walls into the operating stream thereby protecting the bearings and lubrication from the cleaning particles.

3. The method of claim 2, which comprises bleeding air from the compressor, removing cleaning material from such air and introducing such air to protect the bearings and lubrication system.

4. The method of claim 2, which comprises bringing in outside clean air to points inside the seals for protection of the bearings and lubrication.

5. The method of claim 2, in which the cleaning material is microcrystalline.

6. The method of claim 2, in which the cleaning material contains water in chemical combination which evolves in passing -through the rotary engine.

7. The method of claim 2, in which the cleaning material has the property of absorbing liquids.

8. The method of claim 2, in which the cleaning material is a material of the class consisting of alumina-silica minerals and aluminous minerals.

9. The method of claim 8, in which the cleaning mate rial is a mineral of the class of fullers earth, bentonite, bauxite and mixtures thereof.

10. The method of claim 2, which comprises metering' References Cited in the le of this: patent UNITED STATES PATENTS ,11,230,654 Berry June 19, .1917 1,795,348 Schmidt Mar. l0, 1931 2,429,299 Seranovitch Oct. 2l, 1947 2,491,677 McCulloch Dec. 20, 1949 2,627,149 MacCracken Feb. 3, 1953 2,651,887 Graham Sept. 15, 1953 

